Conventional color image-forming device forms correction patch marks of various colors on a rotating member such as a conveying belt, and detects the positions of the correction patch marks to correct the density of each color image and the displacement of different-color images. In such conventional image-forming device, the positions of the correction patch marks are detected by detecting the infrared beam reflected by the rotating member. Further, Japanese Patent Application Publication No. H09-152796 discloses an image-forming device that changes transfer voltage between when forming the correction patch marks and when forming images on a recording medium such as a paper sheet, so that developer is transferred to each object at highest possible efficiency.